Inverse suspension polymerization of water soluble unsaturated monomers



United States Patent INVERSE SUSPENSION POLYMERIZATION OF WATER SOLUBLEUNSATURATED MONOMERS Ralph E. Friedrich and Ralph M. Wiley, Midland, andWalter L. Garrett, Freeland, Mich., assignors to The Dow ChemicalCompany, Midland, Mich., a corporation of Delaware No Drawing. FiledJuly 15, 1957, Ser. No. 671,742

8 Claims. (Cl. 260-23) This invention concerns a polymerization processin which an aqueous solution of a water-soluble unsaturated monomer issuspended in an oil phase and polymerized therein to give polymericproducts in bead form.

Water soluble unsaturated monomers are conventionally polymerized bymass, solution or special oil-in-water suspension techniques.

It has now been discovered that aqueous solutions of water-solubleunsaturated monomers and mixtures thereof can be suspended in an oilphase to form a suspension of globules ranging between 10 microns and 2mms. in diameter and polymerized therein to give polymeric products inbead form having a controlled size. The bead size is controlled by theeliiciency and amount of suspending agent.

The suspending agent is a solid or liquid substance having a lowhydrophile-lyophile balance, i.e., is prepon derantly hydrophobic.Inorganic hydroxy-oxides having substituent hydrocarbonylsilyl,hydrocarbonylsilylene or hydrocarbonylsilylidyne radicals, of the typedescribed and claimed in US. patent application Serial No. 646,- 573,filed March 18, 1957, hereinafter referred to as low hydrophile-lyophilesilanized inorganic hydroxy-oxides or low hydrophile-lyophile silanizedsilica, etc., are particularly useful suspending agents. Other usefulsolid suspending agents include low hydrophile-lyophile kaolin treatedwith rosin amine, bentonite treated with organic ammonium cationyielding reagents, etc. Suspending agents which are useful in the liquidstate include ethyl cellulose and organic polymers which, whilepredominantly hydrophobic, have hydrophilic substituents such as amine,sulfone, carboxy and the like groups. They are dissolved in thehydrophobic dispersion medium. Their low hydrophile-lyophile balancepromotes water-in-oil suspensions. In general, any inert finely dividedsolid or -high molecular weight polymer can be converted to awater-in-oil suspending agent by first determining how it distributesitself when shaken with a mixture of the oil and the aqueous phase to besuspended. If the suspending agent goes entirely into either the oil orthe aqueous .phase, it is either too strongly hydrophobic or toostrongly hydrophilic, and requires surface treatment with a hydrophilicsubstance in the first case and with a hydrophobic substance in thesecond case. In the case of silica and most siliceous clays, theparticles require treatment with a strongly hydrophobic substance suchas an organic amine or an organic silane, preferably of thelong-chaintype. In the case of highly cross-linked organic high polymer particlessuch as styrene latex particles, hydrophilic groups such as amine,sulfone, carboxy, etc. must be introduced in order to increase thehydrophilicity of the surface. The optimum amount and manner ofintroduction of the hydrophile-lyophile balance adjusting groups cannotbe predicted in advance, since it depends on numerous factors such asthe nature of the oil and aqueous phases, the size of the suspendeddroplets desired, and the chemistry of adsorption or reaction betweenthe solid surface and the hydrophile-lyophile halance adjusting agent.In any event, a simple test or trial sufiices to show the suitability ofa proposed suspending agent, or the modification needed. In order toobtain high covering power per gram of suspending agent when a solidsuspending agent is used, a solid having small particles such asbentonite, finely divided silica, etc. is desirable. With coarsersolids, larger amounts must be used in the suspension recipe. The amountof suspending agent used ranges advantageously from about 0.01 weightpercent to about 10 percent, water phase basis, depending upon thesuspending agent and the water-in-oil system. As the proportion ofsuspending agent increases, the polymer bead size decreases.

All known water-soluble unsaturated monomers can be polymerized by theinverse suspension polymerization process of this invention. Suchmonomers include acrylamide, methacrylamide, acrylic acid, methacrylicacid, vinylbenzyl trimethylammonium chloride, alkali metal and ammoniumsalts of 2-sulfoethylacrylate, 2-aminoethyl methacrylate hydrochloride,alkali metal and ammonium salts of vinylbenzyl sulfonate, etc. Aqueoussolutions of the monomers to be polymerized can be varied widely inmonomer content, i.e., from about 5 to weight percent of monomer inwater, depending upon the monomer and the polymerization temperature.The ratio of aqueous monomer phase to oil phase is also widely variable,advantageously from about 5 to 75 weight parts of aqueous phase to to 25parts of oil phase.

The oil phase can be any inert hydrophobic liquid which can be separatedreadily from the polymeric product. of such liquids the hydrocarbons andchlorinated hydrocarbons such as toluene, xylene, o-dichlorobenzene,monochlorobenzene, propylene dichloride, carbon tetrachloride, etc. areadvantageously used. Toluene and xylene are preferred as oil phaseliquids.

The reaction time is widely variable depending upon the catalyst system,and ranges generally between about 10 minutes and two hours attemperatures between about 20 and C.

The reaction is usually carried out at atmospheric or substantiallyatmospheric pressure. However, superatmospheric pressure isadvantageously used when volatile ingredients are involved.

Polymerization initiators including peroxide catalysts such as t-butylhydroperoxide and dimethane sulfonyl peroxide and redox systems such ast-butyl hydroperoxide or potassium persulfate in combination with usualreductants can be used in the practice of this invention. Alternativelyfree radicals can be generated in situ by ultraviolet or X-rays.

In practice, the water-in-oil suspending agent is dissolved or suspendedin the oil phase, depending upon the type used, as indicated. An aqueoussolution of monomer or mixed monomers with or without addedpolymerization initiator is then added to the oil phase with vigorousagitation until the aqueous solution is suspended in the oil phase asglobules ranging between 10 microns and 2 mms. in diameter. The reactiontemperature is then raised to between 20 and 100 C. as desired,preferably with continued mild agitation to prevent separation of phasesor adhesion of polymer beads. Polymerization is initiated by an addedfree radical generator or by ultraviolet or X-radiation, as indicated.The order of addition of reaction media ingredients is not important.The reaction is continued, generally with mild agitation, untilconversion is substantially complete. Polymeric beads are therebyformed, which are separated from the reaction medium, washed and dried.The physical form of the beads and their higher bulk density make forease of separating, washing, drying and subsequent handling. The beadshave a fast solution rate without the danger of breakdown which ispresent with other forms of polymer requiring heating or mechanicalsubdividing to expedite solution thereof. The polymeric beads of thisinvention are useful as binders in coating compositions, and asfiocculating, suspending or thickening agents.

The following examples show ways in which the invention has beenpracticed.

Example 1.Plyacrylamide beads, silanized silica suspending agent Recipe:

800 lbs. aqueous 50 percent acrylnmide, H 5.3 25 p.p.m. potassiumpersulfate 20 p.p.m. tertiary-butyl hydroperoxide acrylamide 20 p.p.m.Z-mercaptoethunol basis 100 p.p.n1. sodium meta-bisulfite 1950 lbs.xylene 0.6 percent low hydrophiie-lyophile siiunizcd silica,

aqueous phase basis The peroxide, persulfate and mercaptan were added tothe aqueous acrylamide. The bisulfite was added to the xylene containedin a glass lined reactor provided with a thermometer and stirrer. Theaqueous acrylamide phase was then added to the oil phase with vigorousagitation to form aqueous droplets containing acrylamide suspended inthe oil phase. Polymerization under a nitro gen atmosphere was initiatedat 30 C. The monomer polymerized adiabatically, and a peak reactiontemperature of 84 C. was noted after minutes. Reaction was continued fora half hour after the peak temperature was noted. Gentle agitation wasmaintained during the polymerization cycle. Acrylamide polymer beadsranging between 75 and 500 microns in particle diameter were separatedfrom the xylene by centrifuging, washed in acetone and dried in a fiashdrier. The polymer viscosity, 0.5 weight percent in water, pH of 3, was22.2 cps. At a concentration of 0.05 lb. of this polyacrylamideflocculant per ton of Peabody coal in a 5.0 percent slurry in water,limed to a pH of 11.0, the settling rate was 2.81 ins. per minute, witha slightly cloudy overhead, as compared with a settling rate of 0.53 in.per minute Without the polyacrylamide fiocculant. The fiocculant wasaded in three increments with three inversion of slurry per increment.

monlum chloride, pH

vinylbenzyl 2000 ppm. ethylene diamine tetraacetic trimethylacidtetrasodlum salt ammonium 2500 p.p.m. tertiary butyl hydroperoxldeghlcinide as s 120 mls, xylene 0.3 g. low hydrophilc-lyophile silnnizedsilica The ethylene diamine tetraacetic acid tetrasodium salt andperoxide were added to the aqueous vinylbenzyl trim'ethylammoniumchloride. The silanized silica was added to the xylene. The aqueousmonomer phase was then added to the oil phase with vigorous agitation toform suspended droplets of aqueous monomer phase in the xylene phase.Polymerization was then initiated in a 76 C. water bath with gentleagitation. Polymerization in the water bath was continued for hours.Polymeric beads ranging in particle diameter between 10 and 50 micronswere separated from the xylene phase, washed and dried. The viscosity ofa 0.5 weight percent solution of the beads in aqueous 2 percent sodiumchloride was 1.54 cps.

was added to the xylene. The aqueous acrylic acid phase was then addedto the oil phase with vigorous agitation to form aqueous dropletscontaining acrylic acid suspended in the oil phase. The suspension waspurged with nitrogen to remove oxygen. Polymerization under a nitrogenatmosphere was initiated and continued for one hour in a water bathmaintained at 70 C. The polyacrylic acid beads so obtained wereseparated, washed and dried. They ranged in particle diameter between 35and microns. A 0.5 weight percent solution of such beads in aqueous 2percent sodium chloride had a viscosity of 35.8 centiposes (pH 7).

Example 4.-P0ly ar (sodium styrene sulfonate) beads, silanized silicasuspending agent Recipe:

40 mls2 aqueous 20 percent ar sodium styrene sulfouate,

108 ppm. potassium persulfate 100 p.p.m. sodium meta-bisulfite mls.xylene 0.2 g. low hydrophilc-lyophile siianized silica The procedure ofExample 3 was followed for a polymerization time of 7 hours. Polymericbeads having a particle diameter ranging between 10 and 100 microns wereobtained. A 0.5 weight percent solution of the beads in aqueous 2percent sodium chloride had a viscosity of 1.99 cps., corresponding to amolecular weight of 330,000.

Example 5.-Cop0lymeric acrylamide-p-vinylbenzyl trimethylammoniumchloride beads, aminated bentonite suspending agent Recipe:

40 mls. 5O 5O mixture of a ueous 50 percent acrylamide and vinylbenzyltrlmethy ammonium chloride 200 ppm. sodium meta-bisulfite 200 ppm.potassium persulfate 8O mls, xylene 0.6 g. low hydrophile-lyophilebcntonitc, organic quaternary ammonium substituted sodium styrenesulfonate basis monomer basis The procedure of Example 2 was followed.Polymeric beads having a particle diameter ranging between 25 and 50microns were obtained. The polymer viscosity, 0.5 weight percent inaqueous 2 percent sodium chloride, was 2.1 cps.

Example 7.Polyacrylamide beads, rosin amine-clay suspending agentRecipe:

jidomls. aqueoltis 5iO percent fnfcrtylamide p.p.m. p0 ass um persu a e200 ppm. sodium meta-bisulfite} acrymmme 80 mls. xylene 0.4 g. lowhydrophile-lyophile rosin amine-treated kaolin The rosin amine-treatedkaolin was suspended in the xylene. Otherwise, a procedure similar tothat of Example 3 was followed. Polyacrylamide beads like those ofExample 1 were obtained.

Example 8.--Polyacrylamide beads, partially sulfa/rated polyvinyltoluenesuspending agent Recipe:

800 mls. aqueous 37 percent acrylnmlde, pH 5.5 20 ppm. potassiumpersulfate 40 p.p.m. 2-mercaptoethnnol 20 p.p.m. tertiary butylhydroperoxide 200 mls. commercial xylene 0.2 percent, aqueous phasebasis. 4 percent sulfonated polyvinyltoluene The sulfonatedpolyvinyltoluene was dissolved in the xylene. The potassium persulfate,Z-mercaptoethanol acrylumide basis and tertiary-butyl hydroperoxide wereadded to the acrylamide. The aqueous phase was added to the oil phasewith vigorous agitation to form a suspension of aqueous dropletscontaining monomer in the oil phase. After purging for minutes withnitrogen, 50 p.p.m. of sodium meta-bisulfite, acrylamide basis, wasadded. The polymerization reaction was initiated at 32 C. After minutesthe reaction temperature was 70 C. An additional 50 p.p.m. of sodiummeta-bisulfite was then added. At the end of 23 minutes the reactiontemperature was 72.7 C. An additional 20 p.p.m. of sodium meta-bisulfiteand 20 p.p.m. t-butyl hydroperoxide was then added. The reaction peakedat 735 C. 25 minutes after the adiabatic reaction was initiated. Thereaction was continued for 32 minutes longer. Polymeric beads similar inappearance to those of Example 1 were obtained. The solution viscosity,0.5 weight percent in water, was 12.8 cps. (pH 3).

Example 9.P0lyacrylamide beads, oil soluble aminated chlorovinyltoluenepolymer suspending agent Recipe:

having an appearance like those of Example 1. Example 10.P0lyacrylamidebeads, gamma radiation initiation Recipe:

mls. aqueous 40 percent acrylamide 80 mls. xylene ins-113312,;sittliitfitiilte' am The aqueous acrylamide was added to the xylene containingthe suspending agent with vigorous agitation to form a suspension ofdroplets of the aqueous phase in the oil phase. The suspension wasexposed to a cobalt source of gamma radiation for one hour while beinggently stirred. The suspension was purged with nitrogen continuouslyduring reaction. The reaction temperature rose from 24 to 40 C. duringexposure to cobalt 60. The polymeric acrylamide beads were separatedfrom the reaction medium, washed in xylene, and dried at 55 C. at 2 mm.pressure. The polymeric beads so obtained 6 What is claimed is: 1. Awater-in-oil suspension polymerization method for making polymers andcopolymers of water-soluble ethylenically unsaturated monomers byforming a water- 5 in-oil suspension of an aqueous solution containingbetween 5 and 80 weight percent of at least one watersolubleethylenically unsaturated monomer in an inert hydrophobic liquid organicdispersion medium containing a suspending agent having a lowhydrophile-lyophile balance, the ratio of aqueous monomer phase to saiddispersion medium ranging between 5 and weight parts of said aqueousphase to 95 to 25 parts of said dispersion medium, and heat-polymerizingthe suspended monomer in the presence of a catalytic amount of apolymerization initiator to obtain a disperse phase polymeric product inbead form.

2. The method of claim 1, wherein the aqueous solution contains between5 and weight percent of monomer.

3. The method of claim 1, wherein the proportion of aqueous dispersephase ranges between 5 and 75 weight percent of the suspension.

4. The method of claim 2, wherein the monomer is acrylamide.

5. The method of claim 2, wherein the monomer is a mixture of acrylamideand p-vinylbenzyl trimethylammonium chloride.

6. The method of claim 2, wherein the monomer is acrylic acid.

7. The method of claim 2, wherein the monomer is at styrene sodiumsulfonate.

8. The method of claim 2, wherein the monomer is p-vinylbenzyltrimethylammonium chloride.

References Cited in the file of this patent UNITED STATES PATENTS2,471,743 Harrison May 31, 1949 2,782,173 Bristol et al. Feb. 19, 19572,824,862 Longley et al. Feb. 25, 1958 OTHER REFERENCES DAlelio:Fundamental Principles of Polymerization, Wiley & Sons (1952), page 212.

Schildknecht (II): "Polymer Processes, Interscience (1956), pages 73, 79and 81.

Schildknecht: Vinyl and Related Polymers, Wiley &

were crosslinked and insoluble in water. They ranged in 50 Sons (1952),pages 314-317.

particle diameter between 75 and 500 microns.

1. A WATER-IN-OIL SUSPENSION POLYMERIZATION METHOD FOR MAKING POLYMERSAND COPOLYMERS OF WATER-SOLUBLE ETHYLENICALLY UNSATURATED MONOMERS BYFORMING A WATERIN-OIL SUSPENSION OF AN AQUEOUS SOLUTION CONTAININGBETWEEN 5 AND 80 WEIGHT PERCENT OF AT LEAST ONE WATERSOLUBLEETHYLENICALLY UNSATURATED MONOMER IN AN INERT HYDROPHOBIC LIQUID ORGANICDISPERSION MEDIUM CONTAINING A SUSPENDING AGENT HAVING A LOWHYDROPHILE-LYOPHILE BALANCE, THE RATIO OF AQUEOUS MONOMER PHASE TO SAIDDISPERSION MEDIUM RANGING BETWEEN 5 AND 75 WEIGHT PARTS OF SAID AQUEOUSPHASE TO 95 TO 25 PARTS OF SAID DISPERSION MEDIUM, AND HEAT-POLYMERIZINGTHE SUSPENDED MONOMER IN THE PRESENCE OF A CATALYTIC AMOUNT OF APOLYMERIZATION INITIATOR TO OBTAIN A DISPERSE PHASE POLYMERIC PRODUCT INBEAD FORM.